European Standards

Standards EN-ISO 10545 and UNI-EN 14411, assimilated by the CEN (European Committee for Standardisation), are valid throughout Europe and apply to all types of tiles: pressed and extruded, glazed and unglazed, in any size and of prime quality only.
General standards
Basic standard UNI EN 14411, which gives definitions, classification, characteristics, and features for designation of the ceramic tiles generally used for covering floors and walls.
Standard ISO 10545-1, which provides for the rules for the composition of the sampling lot.
Standards for testing methods
These standards define the methods for determining the dimensions and surface quality, the physical properties, and the chemical properties.
Standards for product requirements
Ceramic tiles are divided into groups according to their manufacturing method and level of water absorption.
The letter A is used to distinguish tiles that are moulded in a plastic state in an extruder; the body thus obtained is cut into tiles of a pre-established length. They can be glazed or unglazed.
The letter B is used to distinguish tiles manufactured using raw materials reduced to powder or small grains and moulded under high-pressure. They can be glazed or unglazed.
Ceramic tiles are also divided into groups according to their water absorption:
BIa E = 0.5%
BIb 0.5% < E = 3%
Porcelain stoneware usually belongs to class BIa.

tiles with medium water absorption (group II) 3% < E = 10%

The group is subdivided as follows:
3% < E = 6% (group IIa)
6% < E = 10% (group IIb)

tiles with high water absorption (group III) E > 10%.
For each group of products, the product standards define the dimensions, the size tolerance, as well as the mechanical, physical, and chemical characteristics, the appearance, and the designation of the ceramic tiles.
 
European standards (.pdf).

Rules of maintenance for porcelain stoneware (.pdf).